The present invention relates to a closed circuit cooling device for a vacuum pump with moving elements housed in a pump body, the closed circuit having cooling chambers with a fluid flowing through, made in the walls of the pump body, a heat exchanger supplied on one side with the cooling fluid coming from said chambers and on the other with an air flow, and a fluid return between the exchanger and the cooling chambers.
The device is intended in particular for a vacuum pump with two twin screws housed in one and the same cylinder, engaging with one another, and having a motor connected to one of the screws.
Vacuum pumps designed for high performance require cooling, and implementation of cooling devices in accordance with the above definition is known. In general the cooling fluid is water. These closed circuit devices are distinguishable from lost water systems, which at present are no longer acceptable for ecological and economic reasons. They are also distinguishable from direct air systems which are inadequate given the requirements of vacuum pumps from the point of view of the amounts of heat to be removed.
However, the closed circuit devices known until now also have failings when it is a question of equipping vacuum pumps of high performance and compact construction, as are the pumps with two twin screws housed in one and the same cylinder, especially when the profile of the screws is designed so as to obtain maximum efficiency, with a high speed of rotation and as small a size as possible. At any rate, the known closed circuit cooling systems have the drawback of requiring a circulating pump. Moreover, the high performance pumps require a radiator of particularly large dimensions.
The aim of the present invention is therefore to create a cooling device which avoids the above-mentioned failings.
To that end, the device according to the invention is characterised in that the heat exchanger is a condenser, in that the flow of cooling air is generated by a fan driven by the pump motor, and in that the cooling chambers are dimensioned so that the fluid has reached its boiling point at the output thereof.
According to one embodiment, the fan is mounted directly on the shaft of one of the screws and may be placed between the driven screw and the motor.
The condenser can be of the crossed circulation type and have a chamber containing a network of tubes, at least part of which is in an inclined position so as to have the vaporized cooling fluid flowing through from top to bottom, said chamber capable of having a lateral opening in its upper part for input of the air flow and, in its lower part, a connection to the input duct of the fan.
The invention also relates to a vacuum pump with two twin screws housed in one and the same cylinder, engaging with one another, and having a motor connected to one of the screws, and having a cooling device according to the invention.